1. Field of the Invention
The present invention relates to reduction of vibrations of a drive unit for driving a movable member using a piezoelectric transducer that expands and contracts in the prescribed axial direction by applying a prescribed voltage.
2. Description of the Related Art
An impact drive actuator employing a piezoelectric transducer, which corresponds to a linear motion actuator, as a drive mechanism for driving a driven body is known. An example of the drive mechanism employing a conventional impact drive actuator is shown in FIG. 1.
An impact drive actuator 1 is a cylindrical piezoelectric element as a piezoelectric transducer formed of piezoelectric ceramic. Application of saw tooth voltage continuously on the piezoelectric element of the impact drive actuator 1 as shown in FIG. 2 or FIG. 3 enables generation of linear vibrations of, for example, about 60 kHz to 70 kHz.
A movable shaft 2 is fixedly joined at one end thereof to one end surface of the piezoelectric element 1 in the direction of vibrations by means of strong adhesive or the like. A fixing member 3 is fixedly joined to the other end surface of the piezoelectric element 1 also by means of strong adhesive or the like. The fixing member 3 is fixed to a supporting member 4 such as a chassis. The other end of the movable shaft 2 that is not shown in the figure is held by the supporting member loosely to an extent that does not cause rattling.
An optical pickup 5 frictionally holds the movable shaft 2 by clamping the same with a slider 6 provided at one end thereof and a leaf spring 7 that corresponds to a resilient body fixed thereon with a screw 7a. A guide shaft 8 is inserted through and held by a shaft hole 5a formed through the other end of the optical pickup 5. Both ends of the guide shaft 8 are fixed to the supporting member.
The drive mechanism employing the impact drive actuator arranged as described above expands in the direction indicated by an arrow a in FIG. 1 in the period of a shown in FIG. 2 by applying a saw tooth voltage on the piezoelectric element 1, and the movable shaft 2 fixed at one end thereof to the piezoelectric element moves in the direction indicated by an arrow a in FIG. 1. In this case, since the optical pickup 5 is frictionally held and engaged by a frictional holding mechanism of the movable shaft 2 constructed of the leaf spring 7 and the slider 6, the optical pickup 5 moves in the direction c in association with the movement of the movable shaft 2 in the direction indicated by the arrow a. When a voltage to be applied on the piezoelectric element 1 is abruptly changed in the period of b shown in FIG. 2 after a predetermined stop period c has elapsed, the piezoelectric element 1 abruptly contracts in the direction indicated by the arrow b in FIG. 1. In association of abrupt change of the piezoelectric element 1, the movable shaft 2 moves abruptly in the direction indicated by the arrow b. As a result of abrupt movement of the movable shaft 2, an optical pickup frictionally engaged by the movable shaft via the frictional holding mechanism stays in the vicinity of the position where it has been stopped during a stop period c in FIG. 2. By repeating such action, the optical pickup 5 is enabled to move in the direction indicated by an arrow c in FIG. 1.
When a voltage as shown in FIG. 3 is applied on the piezoelectric element 1, the optical pickup 5 moves toward the direction indicated by an arrow d in FIG. 1, which is the direction opposite from the direction of movement described in conjunction with FIG. 2.
The fixing member 3 of the piezoelectric element 1 is, as shown in FIG. 4, fixedly adhered by being fitted into a hole 4a formed on the supporting member 4 such as the chassis by means of an adhesive agent 9. Therefore, vibrations transmitted from the supporting member 4 tends to be transmitted to the piezoelectric element via the adhesive agent 9 and the fixing member 3, which causes a problem in that an unnecessary turbulence vibrations are transmitted to the piezoelectric element and thus accurate vibrations to drive the optical pickup 5 accurately are hindered. There is also a case in which vibrations of the piezoelectric element 1 is transmitted to the supporting member 4 via the fixing member 3 on the contrary, and the piezoelectric element 1 and the supporting member 4 may vibrate sympathetically, which may also hinder accurate vibrations of the piezoelectric element. In this case, frequency of sympathetic vibration is 1/T Hz in the case of FIG. 2 and FIG. 3.
Fixing the fixing member 3 of the piezoelectric element 1 to the supporting member 4 by means of adhesive agent requires management of equipment of adhering operation, the quantity of adhesive agent, and the period of time required for adhesion. In addition, there are problems in that adhesive agent makes disassembly of the piezoelectric element 1 difficult, or adhesive agent attached on other components causes another defective.
Accordingly, it is an object of the present invention to provide a drive unit for driving a movable portion including a vibrating unit that expands or contracts in the predetermined direction by being applied with a predetermined voltage, a movable shaft unit fixed at one end to an end of the vibrating unit and movably supported at the other end, and being moved in the direction of expansion or contraction of the vibrating unit, an engaging unit for frictionally engaging the movable portion with the movable shaft unit, a fixing unit to be fixed at the end of the vibrating unit whereon the movable shaft unit is fixed at the other end, a drive control unit for applying driving voltage for differentiating speed of expansion and contraction of the vibrating unit, and a damping member for supporting the fixing unit in a stationary member with vibrations attenuated.